﻿// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND, 
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED 
// WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
// 
// Copyright (C) 2002 Obviex(TM). All rights reserved.
// 
using System;
using System.IO;
using System.Text;
using System.Security.Cryptography;

/// <summary>
/// This class uses a symmetric key algorithm (Rijndael/AES) to encrypt and 
/// decrypt data. As long as encryption and decryption routines use the same
/// parameters to generate the keys, the keys are guaranteed to be the same.
/// The class uses static functions with duplicate code to make it easier to
/// demonstrate encryption and decryption logic. In a real-life application, 
/// this may not be the most efficient way of handling encryption, so - as
/// soon as you feel comfortable with it - you may want to redesign this class.
/// </summary>
public class RijndaelSimple
{
    /// <summary>
    /// Encrypts specified plaintext using Rijndael symmetric key algorithm
    /// and returns a base64-encoded result.
    /// </summary>
    /// <param name="plainText">
    /// Plaintext value to be encrypted.
    /// </param>
    /// <param name="passPhrase">
    /// Passphrase from which a pseudo-random password will be derived. The
    /// derived password will be used to generate the encryption key.
    /// Passphrase can be any string. In this example we assume that this
    /// passphrase is an ASCII string.
    /// </param>
    /// <param name="saltValue">
    /// Salt value used along with passphrase to generate password. Salt can
    /// be any string. In this example we assume that salt is an ASCII string.
    /// </param>
    /// <param name="hashAlgorithm">
    /// Hash algorithm used to generate password. Allowed values are: "MD5" and
    /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
    /// </param>
    /// <param name="passwordIterations">
    /// Number of iterations used to generate password. One or two iterations
    /// should be enough.
    /// </param>
    /// <param name="initVector">
    /// Initialization vector (or IV). This value is required to encrypt the
    /// first block of plaintext data. For RijndaelManaged class IV must be 
    /// exactly 16 ASCII characters long.
    /// </param>
    /// <param name="keySize">
    /// Size of encryption key in bits. Allowed values are: 128, 192, and 256. 
    /// Longer keys are more secure than shorter keys.
    /// </param>
    /// <returns>
    /// Encrypted value formatted as a base64-encoded string.
    /// </returns>
    public static string Encrypt(string   plainText,
                                 string   passPhrase,
                                 string   saltValue,
                                 string   hashAlgorithm,
                                 int      passwordIterations,
                                 string   initVector,
                                 int      keySize)
    {
        // Convert strings into byte arrays.
        // Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8 
        // encoding.
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes  = Encoding.ASCII.GetBytes(saltValue);
        
        // Convert our plaintext into a byte array.
        // Let us assume that plaintext contains UTF8-encoded characters.
        byte[] plainTextBytes  = Encoding.UTF8.GetBytes(plainText);
        
        // First, we must create a password, from which the key will be derived.
        // This password will be generated from the specified passphrase and 
        // salt value. The password will be created using the specified hash 
        // algorithm. Password creation can be done in several iterations.
        PasswordDeriveBytes password = new PasswordDeriveBytes(
                                                        passPhrase, 
                                                        saltValueBytes, 
                                                        hashAlgorithm, 
                                                        passwordIterations);
        
        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = password.GetBytes(keySize / 8);
        
        // Create uninitialized Rijndael encryption object.
        RijndaelManaged symmetricKey = new RijndaelManaged();
        
        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;        
        
        // Generate encryptor from the existing key bytes and initialization 
        // vector. Key size will be defined based on the number of the key 
        // bytes.
        ICryptoTransform encryptor = symmetricKey.CreateEncryptor(
                                                         keyBytes, 
                                                         initVectorBytes);
        
        // Define memory stream which will be used to hold encrypted data.
        MemoryStream memoryStream = new MemoryStream();        
                
        // Define cryptographic stream (always use Write mode for encryption).
        CryptoStream cryptoStream = new CryptoStream(memoryStream, 
                                                     encryptor,
                                                     CryptoStreamMode.Write);
        // Start encrypting.
        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);
                
        // Finish encrypting.
        cryptoStream.FlushFinalBlock();

        // Convert our encrypted data from a memory stream into a byte array.
        byte[] cipherTextBytes = memoryStream.ToArray();
                
        // Close both streams.
        memoryStream.Close();
        cryptoStream.Close();
        
        // Convert encrypted data into a base64-encoded string.
        string cipherText = Convert.ToBase64String(cipherTextBytes);
        
        // Return encrypted string.
        return cipherText;
    }
    
    /// <summary>
    /// Decrypts specified ciphertext using Rijndael symmetric key algorithm.
    /// </summary>
    /// <param name="cipherText">
    /// Base64-formatted ciphertext value.
    /// </param>
    /// <param name="passPhrase">
    /// Passphrase from which a pseudo-random password will be derived. The
    /// derived password will be used to generate the encryption key.
    /// Passphrase can be any string. In this example we assume that this
    /// passphrase is an ASCII string.
    /// </param>
    /// <param name="saltValue">
    /// Salt value used along with passphrase to generate password. Salt can
    /// be any string. In this example we assume that salt is an ASCII string.
    /// </param>
    /// <param name="hashAlgorithm">
    /// Hash algorithm used to generate password. Allowed values are: "MD5" and
    /// "SHA1". SHA1 hashes are a bit slower, but more secure than MD5 hashes.
    /// </param>
    /// <param name="passwordIterations">
    /// Number of iterations used to generate password. One or two iterations
    /// should be enough.
    /// </param>
    /// <param name="initVector">
    /// Initialization vector (or IV). This value is required to encrypt the
    /// first block of plaintext data. For RijndaelManaged class IV must be
    /// exactly 16 ASCII characters long.
    /// </param>
    /// <param name="keySize">
    /// Size of encryption key in bits. Allowed values are: 128, 192, and 256.
    /// Longer keys are more secure than shorter keys.
    /// </param>
    /// <returns>
    /// Decrypted string value.
    /// </returns>
    /// <remarks>
    /// Most of the logic in this function is similar to the Encrypt
    /// logic. In order for decryption to work, all parameters of this function
    /// - except cipherText value - must match the corresponding parameters of
    /// the Encrypt function which was called to generate the
    /// ciphertext.
    /// </remarks>
    public static string Decrypt(string   cipherText,
                                 string   passPhrase,
                                 string   saltValue,
                                 string   hashAlgorithm,
                                 int      passwordIterations,
                                 string   initVector,
                                 int      keySize)
    {
        // Convert strings defining encryption key characteristics into byte
        // arrays. Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8
        // encoding.
        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);
        byte[] saltValueBytes  = Encoding.ASCII.GetBytes(saltValue);
        
        // Convert our ciphertext into a byte array.
        byte[] cipherTextBytes = Convert.FromBase64String(cipherText);
        
        // First, we must create a password, from which the key will be 
        // derived. This password will be generated from the specified 
        // passphrase and salt value. The password will be created using
        // the specified hash algorithm. Password creation can be done in
        // several iterations.
        PasswordDeriveBytes password = new PasswordDeriveBytes(
                                                        passPhrase, 
                                                        saltValueBytes, 
                                                        hashAlgorithm, 
                                                        passwordIterations);
        
        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = password.GetBytes(keySize / 8);
        
        // Create uninitialized Rijndael encryption object.
        RijndaelManaged    symmetricKey = new RijndaelManaged();
        
        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;
        
        // Generate decryptor from the existing key bytes and initialization 
        // vector. Key size will be defined based on the number of the key 
        // bytes.
        ICryptoTransform decryptor = symmetricKey.CreateDecryptor(
                                                         keyBytes, 
                                                         initVectorBytes);
        
        // Define memory stream which will be used to hold encrypted data.
        MemoryStream  memoryStream = new MemoryStream(cipherTextBytes);
                
        // Define cryptographic stream (always use Read mode for encryption).
        CryptoStream  cryptoStream = new CryptoStream(memoryStream, 
                                                      decryptor,
                                                      CryptoStreamMode.Read);

        // Since at this point we don't know what the size of decrypted data
        // will be, allocate the buffer long enough to hold ciphertext;
        // plaintext is never longer than ciphertext.
        byte[] plainTextBytes = new byte[cipherTextBytes.Length];
        
        // Start decrypting.
        int decryptedByteCount = cryptoStream.Read(plainTextBytes, 
                                                   0, 
                                                   plainTextBytes.Length);
                
        // Close both streams.
        memoryStream.Close();
        cryptoStream.Close();
        
        // Convert decrypted data into a string. 
        // Let us assume that the original plaintext string was UTF8-encoded.
        string plainText = Encoding.UTF8.GetString(plainTextBytes, 
                                                   0, 
                                                   decryptedByteCount);
        
        // Return decrypted string.   
        return plainText;
    }
}
